1. Field of the Invention
The present invention relates to a liquid discharging apparatus for discharging liquid by generating a bubble by the application of heat energy on the liquid, and more particularly to a liquid discharging apparatus having a movable member which displaces by taking advantage of generation of the bubble.
In this respect, xe2x80x9crecordingxe2x80x9d in the present invention is not only to impart a significant image such as characters and patterns onto a recording medium, but also to impart a meaningless image including any other than patterns or the like.
2. Related Background Art
Conventionally, there has been known an ink jet recording method, a so-called bubble jet recording method, in which, in a recording apparatus such as printers, the bubble is generated by imparting energy such as heat to liquid ink in a flow path, and the ink is discharged through discharging ports by means of an operating force based on a sudden volume change caused by the occurrence of the bubble to cause the ink to adhere onto a recording medium for forming an image. A recording apparatus using this bubble jet recording method is generally provided, as disclosed in specification of U.S. Pat. No. 4,723,129 or the like, with discharging ports through which the ink is discharged, flow paths communicated to these discharging ports, and electrothermal transducers as energy generating means for discharging the ink provided within the flow paths.
Such a recording method has many excellent advantages that it is possible to easily obtain a recorded image with high resolution and further, a color image with a small-sized apparatus because a high-quality image can be recorded at high speed and in low noise and a head in which this recording method is performed can be at high density provided with discharging ports for discharging the ink. For this reason, this bubble jet recording method has been utilized for many office equipment such as printers, copying machines and facsimile apparatuses in recent years, and further for industrial systems such as textile printing apparatuses.
As the bubble jet technique has been utilized for products in many fields as described above, the following various requests have been further increasing in recent years.
In order to obtain a high-quality image, there are proposed driving conditions for allowing a liquid discharging method in which excellent ink based on stable occurrence of the bubble can be performed at high speed, and a method in which the shape of flow paths has been improved in order to obtain a liquid discharging head having a faster refill speed of the discharged liquid within the flow paths in view of high-speed recording.
In addition to such a head, there has been disclosed, in Japanese Patent Application Laid-Open No. 6-31918, an invention having configuration to prevent back waves (pressure toward a direction opposite to the direction toward the discharging ports), which becomes loss energy in the discharging, focusing attention on the back waves for occurring with the generation of the bubble. The invention specified in this publication is that a triangular portion of a triangular plate-shaped member is caused to oppose to a heater for generating the bubble. According to this invention, the plate-shaped member restrains the back waves temporarily and slightly. This invention, however, does not touch on correlation between the growth of the bubble and the triangular portion, but the invention includes the following problems because it has no idea thereof.
That is, according to the invention specified in the above-described publication, the heater is located at the bottom of a concave portion and cannot be linearly communicated to the discharging ports, and therefore, the shape of liquid droplets cannot be stabilized. Further, since the growth of the bubble is allowed around the vertex of the triangle, the bubble grows from one side of the triangular plate-shaped member to the entire opposite side, with the result that normal growth of the bubble in the liquid is completed as if there existed no plate-shaped members. Therefore, the existence of the plate-shaped member would have nothing to do with growing the bubble. On the contrary, since the entire plate-shaped member is enclosed with the bubble, refilling to the heater located at the concave portion causes a turbulent flow in a shrinkage state of the bubble to thereby accumulate fine bubbles within the concave portion, thus violating the principle itself in which discharging is performed based on growing the bubble.
On the other hand, EP Patent Application Laid-Open No. 436047A1 has proposed an invention in which a first valve for intercepting a relation between a discharge port-neighboring area and the bubble generating unit and a second valve for completely intercepting a relation between the bubble generating unit and an ink supply unit are caused to be alternately opened and closed (FIGS. 4 to 9 of EP436047A1). In this invention, however, since these three chambers are partitioned into two chambers each, ink following the liquid droplet becomes large trailing during discharging, and there are a considerably multiplicity of satellite dots as compared with the normal discharging system in which growth of bubble, shrinkage (contraction) and bubble disappearance are performed (it is inferred that an effect of backward movement of meniscus by bubble disappearance could not be used). During refilling, although the liquid is supplied to the bubble generating unit with the bubble disappearance no liquid can be supplied to the discharge port-neighboring area until the next expanding is generated, and therefore, variations in discharged liquid droplets are not only large, but also the discharge response frequency is very smallxe2x80x94being not at practical level.
There have been proposed, by the present applicant, a number of inventions using a movable member (a plate-shaped member having a free end closer to the discharge port side than a support, or the like) capable of effectively contributing to discharging of liquid droplets quite unlike the above described prior art. Of these inventions, a Japanese Patent Application Laid-Open No. 9-48127 discloses an invention in which the upper limit of displacement of the movable member is regulated in order to prevent behavior of the above described movable member from being slightly confused. Also, a Japanese Patent Application Laid-Open No. 9-323420 discloses an invention in which an upstream common liquid chamber is shifted on the free end side of the movable member, that is, on the downstream side by the utilization of the advantage of the movable member to enhance the refilling ability. These inventions do not focus attention on individual elements concerning formation of the liquid droplet by the entire bubble and correlation of those elements because, as a precondition for the invention, there has been supposed a form in which the growth of the bubble is released on the discharge port side at a stroke from a state in which it is temporarily wrapped by the movable member.
As the next stage, the present applicant has disclosed, in a Japanese Patent Application Laid-Open No. 10-24588, an invention in which a part of the bubble generating area is released from the movable member, as an invention (acoustic wave) in which attention is focused on the growth of the bubble due to propagation of pressure waves as an element relating to the discharging of liquid. Even in this invention, however, no attention has been focused on individual elements concerning formation of the liquid droplet itself by the entire bubble and correlation of those elements because attention is focused only on the growth of the bubble when the liquid is discharged.
Although it is known that the front portion (edge shooter type) of the bubble due to conventionally-known film boiling greatly affect the discharging, no one has focused attention on causing this portion to more efficiently contribute to formation of the discharged liquid droplet, but the present inventors have earnestly studied to elucidate these technical problems.
In such a study process, in a movable member having a free end capable of displacing with growth of the bubble, there was a case where the bubble go round from the tip end side of the movable member under a certain condition in the displacement process. As its details, the following phenomenon was confirmed in the technical analysis of the invention.
More specifically, in a process of growth of the bubble for discharging liquid droplets, and upward displacement of the movable member brought about by the growth of the bubble, the displacement of the movable member cannot catch up with the growth of the bubble, but the grown a bubble is going to go on to the upper surface of the movable member. Under a certain condition, for example, in the case where the liquid supply-side flow path resistance is very low and the liquid is prone to move in that direction, it was observed that the bubble go round to the rear of nozzle flow path along with the movement of the liquid to the rear of nozzle flow path caused by displacement of the movable member.
When a liquid flowing force to the rear of nozzle flow path is produced in the displacement process of the movable member, an effect of the movable member of efficiently directing the discharging energy caused by the growth of the bubble toward the discharge port may be reduced.
Thus, the present inventors have newly found, in the nozzle flow path for a liquid discharging head using a movable member having a free end, a liquid flow to the rear of the flow path in a process of valve displacement, and configuration of the flow path to prevent the bubble from going round to the rear of the flow path due to the liquid flow, whereby the discharging efficiency forward of the nozzles is improved, and meniscus return and early stabilization of the filling liquid during refilling are performed.
The present invention obtained in such study process as described above is characterized in that, there is provided a liquid discharge method through a liquid discharge head provided with a liquid flow path having a bubble generating area, in which a bubble is generated from liquid; a heater for generating heat energy to generate and grow the bubble; a discharge port which communicates to the liquid flow path and is a portion for discharging the liquid; a movable member provided in the bubble generating area, having a free end which shifts along with growth of the bubble; and a liquid flow regulating portion for regulating liquid flow in a direction opposite to the discharge port in a displacement process of the movable member and the growth of the bubble, having a step of forming space substantially closed in the liquid flow path having the bubble generating area except for the discharge port by bringing the free end of the movable member in the displacement process, close to the liquid flow regulating portion without substantially contacting each other.
The above described method is characterized in that, in a process in which the free end of the movable member shifts, the liquid flow in a direction opposite to the discharge port is sheared when the free end is passing through the vicinity of the liquid flow regulating portion.
Further, the method is characterized by having a process in which the bubble shrinks in a state where the closed space is formed.
The method is characterized in that, in the process in which the bubble shrinks, the greater part of the liquid which moves along with the shrinkage of the bubble is directed toward the upstream side from the discharge port and meniscus is suddenly drawn into the discharge port.
Further, the method is characterized in that the movable member is spaced apart from the liquid flow regulating portion along with the shrinkage of the bubble, whereby a liquid flow toward the downstream side facing the discharge port is caused in the bubble generating area to thereby suddenly brake the meniscus to be drawn in.
Also, according to the present invention, there is provided a liquid discharge head having: a liquid flow path having a bubble generating area, in which a bubble is generated from liquid; a heater for generating heat energy to generate and grow the bubble; a discharge port which communicates to the liquid flow path and is a portion for discharging the liquid; a movable member provided in the bubble generating area, having a free end which shifts along with the growth of the bubble; and a liquid flow regulating portion for regulating liquid flow in a direction opposite to the discharge port in the displacement process of the movable member and the growth of the bubble, in which the free end of the movable member in the displacement process and the liquid flow regulating portion are brought close to each other without actually bringing them into contact with each other, whereby the liquid flow path having the bubble generating area becomes space substantially closed except for the discharge port, and wherein there are arranged the movable member and the liquid flow regulating portion such that a bubble at the maximum growth does not intercept the interior of the space with reference to the fluid flow.
The above described head is characterized in that the liquid flow regulating portion is provided in the vicinity of the discharge port side of the displacement area of the free end of the movable member.
Further, the liquid discharge head is characterized in that there has been provided a displacement regulating unit for regulating displacement of the movable member after the formation of the closed space. This enables the refilling property to be enhanced by restraining the movement of the liquid to the upstream side after the formation of the closed space.
Further, the liquid discharge head is characterized in that there has been provided a side regulating unit, at least one portion of which substantially comes into contact with both side edges of the movable member in the displacement process, for regulating a bubble generated from the bubble generating area. This enables, even if a clearance between the side walls of the liquid flow path and the movable member is set loose, the liquid flow from the clearance to the upstream side and the growth of a bubble to be restrained.
Further, the liquid flow regulating portion is characterized in that it is located closer to the discharge port side than the free end of the movable member, and, when viewed from the discharge port, the free end of the movable member in the displacement process is covered and the liquid flow regulating portion is kept at such a distance as not to bring it into contact with the free end.
Further, the liquid discharge head is characterized in that, in the process in which the free end of the movable member shifts, the locus portion of the free end when the free end is passing through the vicinity of the liquid flow regulating portion is narrow space. This causes the liquid flow on the upstream side due to upward displacement of the movable member to become faster, and therefore, the displacement speed of the movable member is also made faster.
Further, the upstream-side portion of the liquid flow regulating portion is characterized by having a tapered configuration which tapers downwards from the flow path ceiling. This enables the flow path resistance during refilling from the upstream side to be reduced. Further, since the width of the liquid flow regulating portion in the flow path direction can be reduced, it is possible to secure a large flow path volume on the discharge port side with the liquid flow regulating portion as the border, which is useful to discharge large liquid droplets.
Further, the movable member is characterized by having a protruded portion which protrudes from the surface of the movable member on the heater side in the vicinity of the bubble generating area. This enables pressure waves when the bubble is generated not to affect the upstream side as far as possible.
According to the configuration described above, since it is possible to effectively take advantage of the flow of the liquid in the vicinity of the discharge port caused by the growth of the bubble and start of bubble disappearance for formation of liquid droplets peculiar to the ink jet, and to reduce the amount of backward movement of meniscus, time required for returning of the meniscus can be greatly shortened, and the dependence characteristic on response frequency can be improved. Particularly, due to the position of the liquid flow regulating portion relative to the movable member, the liquid flow on the upstream side and the growth of the bubble, which bring a minus effect to the refilling property, are intercepted smoothly and quickly without bringing the movable member in the displacement process into contact to thereby substantially make the liquid flow path having the bubble generating area into substantially closed space, and thus the discharging energy due to the growth of the bubble can be effectively directed toward the discharge port.
As regards the other effects of the present invention, they will be obvious from the description of each embodiment.
In this respect, xe2x80x9cupstreamxe2x80x9d and xe2x80x9cdownstreamxe2x80x9d used in the description of the present invention are represented as expression concerning a direction of flow of the liquid from the supply source thereof toward the discharge port through the bubble generating area (or movable member), or the direction in this configuration.
Also, xe2x80x9cdownstream sidexe2x80x9d concerning the bubble itself means the downstream side concerning the above described direction of flow or the direction in the above described configuration with respect to the center of the bubble, or a bubble which is generated in an area on the downstream side of the center of area of the heater.
A xe2x80x9csubstantially contactxe2x80x9d between the movable member and the side regulating unit, which is expressed in the present invention, does not always mean that the movable member and the side regulating unit are brought into tight contact with each other, but also includes that the movable member comes unlimitedly close to the side regulating unit.